In the case of a known machine of this kind (West German O/S No. 23 49 732) the wires forming the strutting are continuously bent and are subsequently welded to chord rods intermittently. In order to be able to coordinate these two working procedures, which run with different rhythms, a stock of the already bent strut wire is bent into a loop running from the bending station for this wire to the welding station for the welding of this wire to the chord rods. The size of the loop to be formed is left to the judgement by eye and the experience of the machine operator. The free space for the formation of the loop must be sufficiently large in order to avoid permanent deformations of the strut material while running round the loop. Such permanent deformations transversely to the plane of the strutting would be extremely disadvantageous in the end product, in particular because the girders to be produced should have a planar structure. Three-dimensional girders cannot be produced at all with the known machine because, with the formation of a loop of wire strutting which is acceptable in practice, only one arrangement of struts can be fed to the welding station.